Priesthood

He was ordained on 2 June 1906 in Arequipa. Worked as a parish priest from 1906 until 1910 in Arica, nowadays in Chile. He was expelled by the Chilean Government when it claimed the province of he was working in. He became Vice-rector of the Seminary of Arequipa, in 1910, where he stayed for ten years until 1920. He was named sacristan of the cathedral of Arequipa 1916 - 1920. He worked as staff member of El Deber, oldest newspaper in southern Peru, 1916 - 1940 and its director 1928 - 1940.

Episcopate

Guevara was appointed Bishop of Trujillo by Pope Pius XII on 15 December 1940. When the diocese of Trujillo was elevated to an archdiocese he became its first archbishop on May 23, 1943. Appointed as Military Vicars of Peru on January 13, 1945 and retained that office until his death. Transferred to the metropolitan see of Lima on 16 December 1945.